Resistor bulb



April 23, 1946; F. G. KELLY 2,398,892

REsIsToR'BULB Filed July 8, 1943 Jnnentr 7 Frederz'ckGK ell y 'mm 11 [Mt/5'.

(Ittorneg Patented Apr. 23, 1946 RESISTOR BULB Frederick G. Kelly, West Orange, N. J., assignor to Thomas A. Edison, Incorporated, West Orange, N. J., a corporation of New Jersey Application July 8, 1943, Serial No. 493,947

14 Claims.

This invention relates to electrical resistor bulbs, and more especially to an improved construction of such bulbs.

It will be understood that these bulbs comprise a temperature-responsive resistance element enclosed by a protective casing or sheath, and that they measure and detect temperature changes of the medium into which the sheath is immersed in terms of the variation i the resistance of that resistance element in response to the temperature changes of that medium.

It is an object of my invention to provide an improved construction of resistor bulb which is highly economical to manufacture.

It is another object to provide an improved construction of resistor bulb which is very easy to assemble.

It is another object to provide an improved construction of resistor bulb which is capable of withstanding heavy shock and vibration over long periods of service, and which is especially adapted for long and dependable service on aircraft.

Another object is to provide an improved construction of resistor bulb wherein the active resistor element thereof is readily removable for replacement.

A yet further object of my invention is to provide an improved resistor bulb which is characterized by a small time lag and small error.

These and other objects of my invention will more fully appear from the following description and the appended claims.

In the description of my invention reference is had to the accompanyin drawing, of which:

Figure 1 is an axial view, partly in section and partly broken away, of a preferred embodiment of resistor bulb according to my invention;

Figure 2 is an elevational View of the resistor unit of my invention as it appears when removed from the casing:

Figure 3 is an end view of the base of the resistor bulb;

Figure 4 is a sectional view taken on the line 4-4 of Figure 1;

Figure 5 is a sectional view taken on the line 5-5 of Figure 1;

Figure 6 is a. sectional view taken on the line B6 of Figure 1; and

Figure 7 is a diagrammatic view of the electrical circuit of the resistor bulb.

The casing for the resistor bulb shown in the accompanying drawing comprises a metal base member I having an externally threaded section section lb. This base member is provided with a central axial bore 2 that extends therethrough. The bore is threaded at the outer end of the bulb, as at 3, and is reduced in diameter at two different points to form an intermediate annular shoulder 4 and a second shoulder 5 at the end of the section la. Engaging the bore at the end of the section la is a metal tubular sheath 6. This sheath has a flanged end 611 which fits the shoulder 5, and is sealed and secured to the base member as by silver soldering. The end of the sheath is sealed bya disk 6b which may be an integral part of the sheath or be a separate element secured thereto also by silver soldering.

The casing above described serves as a protec tive housing for a temperature-responsive resistanceunit 8. In practice, it will be understood that the bulb will be mounted by applying a wrench to the hexagonal section lb and threading the base section la into the wall of a container where temperature measurement are to be made, such as of a carburetor, oil jacket or engine oil case. The sheath 6 will then project into the medium whose temperature is to be measured and will serve to seal and protect the temperatum-responsive unit 8 from direct contact with that medium. My invention resides principally in the construction of the resistance unit 8 and in its mechanical and thermal association with the casing of the bulb, and it is a feature of my invention to provide a simple form of resistance unit which may be removably mounted in the casing and which, when in mounted position, will have a close thermal association with the wall of the sheath 6 so that the resistance unit will respond rapidly to changes in the temperature of the surrounding medium.

The resistance unit 8 comprises a core 9 onto which there is wound a coil ID of temperatureresponsive wire which may, for example, be wire made substantially of pure nickel and be app mately .002" in diameter. The core 9, which is to be made of a non-organic insulating material, is provided in fiat strip or bar form. By using a core of this form there are secured several distinct advantages: (1) it permits the core to be made of laminated fiat mica, which is a preferred material from the standpoint of economy, strength, non-frangibility' and ease of fabrication; (2) by so making the core of mica and providing it with a non-circular cross section, there is eliminated the need for pre-grooving the core, for by winding the resistance wire under tension I it will indent the corners of the core and become la and a non-circular-for example, hexagonal embedded thereinto and held firmly in place; and

(3) by using a core of laminated material there is provided a simple support and insulation for a lead Illa to the inner end of the resistance coil it since this lead may be interposed between the laminations of the core as i shown in the drawing. Yet additionally, the use of a core of b r form has the distinct advantage of permitting a close thermal coupling between the resistance coil and the sheath to be attained by simple and ef fective means, as will hereinafter appear.

The core 9 extends from within the base member l through substantially the full length of the sheath 6 and is made nearly as wide as the internal diameter of the sheath. The separate laminations of the core, of which there are preferably two, are secured together at the inner end of the bulb by a rivet ll. At the base end of the bulb the core is anchored to a cylindrical plug 13 made of a hard insulating material such as that known commercially as Isolantite. This plug has apertures receiving two terminal pins M. The pins are glass-sealed .to the plug and are made of a suitable material having approximately the coefiicient of expansion .of glass so that the plug may not be broken when subjected to a wide range of temperature. The inner ends of the terminal pins have heads I 4a to which a pair of metal standards 15 are welded. These standards have inwardly extending lugs Il a which through and are clamped to the core to secure the core to the plug i3. Additionally, the standards have respective lugs 15b to which the leads of the resistance unit are connected. The lead iila above-mentioned is for instance passed through a hole 12 in one of the laminations at the inner end of the bulb, is then extended between the laminations to the base end of the bulb, and is then passed through a hole I? in one of the core laminations to make connection with one of the lugs 15?). Between the other lead idb of the resistance coil ID and the other of the lugs [51) there is however interposed a coil I8 which is made of a glass fiber insulated wire having a substantially zero coeflicien-t of resistance such as of constantan. For instance, the lead lob may be threaded through a hole IS in the core 9 and be connected to a terminal 20 which is held to the core by a rivet 2i, and the coil i8 ma then be connected at one end to this terminal and at the other end to the terminal lug r lib. The coil l8 may be mounted onto the core by being bent in U form and having the end portions thereof passed through and snugly fitting a pair of holes 22 provided in the core. The function of the coil I8, which is well known, is to enable the temperature coefficient of the resistance unit to be set to a predetermined value by proportioning the total ohmage of the unit between the resistance coil IU of high temperature coefficient material and the coil N3 of low temperature coefficient material.

The plug l3 has an annular flange 13a which is clamped against the interior shoulder 4 of the base member I by an externally threaded sleeve 23 which is threaded into the bore of the base member I. Between the shoulder 4 and the flange Mia, and this flange and sleeve 23, there are interposed respective Washers 24 which are made of soft metal to serve as sealing rings for hermetically enclosing the interior of the bulb from the outside atmosphere, The sleeve 23 extends from the base member I to surround the terminal pins M, and serves as a socket for an electrical connector plug not shown.

An important feature of my invention lies in providing a pair of resilient heat-conducting members 25 between the resistance coil and the sheath 3. Since the core 9 is in the form of a flat strip, these members are permitted to have very simple shape, and may be formed from strips of flat metal stock simply by bending up the side portions from such strips. Each member thus comprises a flat base portion 25a and a pair of side fins 25b. The flat base portions 25a lie adjacent the opposite flat sides of the esistance coil 1a but are isolated electrically from the coils by thin intervening strips 28 of insulation such as of mica. The side fins 2% are curved inwardly so as to conform to the interior surface of the sheath 6. In their natural unrestrained positions, however, the fins spread out beyond the walls of the sheath. Thus, when the resistance unit 8 is in mounted position, the sheath holds the fins inwardly under strain and the fins exert pressure against the wall of the sheath to assure a positive even contact therewith; by the same token, the flat portions 25a of the conducting members are pressed firmly against the insulating members 26 and maintained in close thermal association with the resistance coil If The conducting members 25 and intervening insulating strips 26 are connected to the core 9 so as to constitute a permanent part of the resistance unit 8. The connection of these elements to the core is made however at only one point, preferably at the inner end of the core, as by the rivet H. The advantage in so connecting the members and 26 to the core at only one point is that it leaves them free from longitudinal restraint so that they may conform evenly to the adjacent surfaces of the sheath and resistance coil when the unit 8 is in mounted position. In order though that forces will not tend to be exerted on the members 25 to cause the side fins 25b to buckle and lose their shape from normal handling of the unit 8 before it is mounted in the sheath, the members '25 are connected to the core through the medium of flat lugs 21 which extend from the flat portions of the members beyond the side fins thereof. For instance, before the resistance unit 8 is installed in the sheath, the members and 26 will spring out from the sides of the coil as is shown in Figure 2, but the members 25 maintain their normal shape throughout their effective length.

It will be understood that to install the resistance unit 8 it is only necessary to slide it through the base member I into the sheath 6, with the members 25 bearing slidingly against the interior surface of the sheath, and then to screw the sleeve 23 in place. Vice versa, to remove the resistance unit, it is only necessary to unscrew the sleeve and then withdraw the unit. While the unit is so readily removable, it will be observed that no sacrifice is made in the thermal coupling of the unit to the enclosing sheath 6.

The members 25 are made of a metal having a high conductivity and a substantial resilience. I find for example that the heat conductivity of the material used for these members should be of the order of .5 calorie per degree C. per square p r 01111. per second, or more. A preferred material which I use is silver, which has a heat conductivity of the order of 1 (in the same units) although hard-drawn copper or aluminum may be suitable. Typically, the flat silver stock from which the members 25 are made may be .002" thick.

athermal conductitvity not in excess of ,07 (in .the same units) are satisfactory. The sheath is .made with small wall thickness, typically .012". In using such alloys of such small thickness, the sheath has small longitudinal heat conduction, typically of the order of .0011 calorie per degree C. per second. On the other hand, the small thickness of the sheath and the close thermal coupling which the sheath has with the resistance coil, as provided by the conducting members 25,

serve to give a, high transverse heat conduction Y from the surrounding medium to the resistance coil. Yet the heat-conducting members have relatively small thermal capacity, typically about one-fourth the thermal capacity of the sheath. As a result of the small longitudinal heat conduction of the sheath there is small heat loss to the, base of the bulb and small error in indicationthat is, the resistance coil attains closely thetemperature of the medium surrounding the sheath. Furthermore, as a result of the high transverse heat conduction and relatively small thermal capacity abovementioned, the resistance coil responds. to changes in the temperature of themedium surrounding the sheath with small time lag; 1 I

.As a further feature in the construction of the resistor bulb above described, it will be observed that due to the resilient character of the members 25, and the fact that they are interposed between the resistance coil and the sheath under strain, these members serve to provide a firm but yieldable support for the resistance coil and do so continuously along the Whole length of the coil. As a result it is found that the resistor bulb is rendere'd'capable of withstanding heavy shock and vibration over long periods of service without causing the resistance Wire of the coil ID to be broken or otherwise damaged.

I have. herein shown and described a preferred embodiment of my invention but it will be understoodthat this embodiment is subject to changes and modifications without departure from the scope of my invention which I endeavor to express according to the following claims.

I claim:

1. A resistor bulb adapted for response to changes in temperature of a medium to which the bulb is thermally exposed, comprising a casing adapted to be immersed in said medium, said casing having a mounting base at one end; and a resistance unit mounted in said casing and removable therefrom by way of said base, said unit comprising a temperature-responsive resistance element extending lengthwise of said casing and spaced from the wall thereof, and a resilient heatconducting means thermally associated with said resistance element and contacting said wall, said heat-conducting means being permanently secured to said unit and adapted to slide against said wall upon mounting and removing the unit into and from the casing, and said heat-conducting means exerting pressure against both said resistance element and the wall of said casing.

2. In a resistor bulb adapted for response to changes in temperature of a medium to which the 3 bulb is thermally exposed, said bulb including a protective casing for immersion in said medium: the combination of a resistance element within said casing, said element beingspaced from the wall thereof; and a resilient heat-conducting means interposed between said resistance element and the wall of said casing, said heat-conducting means contacting said casing and being yield able in compression, and said heat-conducting means being held under strain by said casing and yieldably supporting said resistance element within said casing.

3. In a resistor bulb adapted for response to changes in temperature of a medium to which the bulb is thermally exposed, said bulb including a protective sheath for immersion in said medium: the combination of a resistance coil within said sheath, said coil being spaced from the wall thereof; and compressibly yieldable heatconducting spring means interposed between said resistance coil and said sheath, said heat-conducting means being in close thermal proximity with said resistance coil throughout the length thereof and having an exterior surface conforming to and engaging the interior surface of said sheath.

4. In a resistor bulb adapted for response to changes in temperature of a medium to which the bulb is thermally exposed, said bulb including a protective sheath for immersion in said medium: the combination of a flat core element within said sheath, said core element extending lengthwise of said sheath and having its greater dimension in cross section equal substantially to the internal diameter of said sheath; a coil of temperature-responsive resistance wire wound on said core element; and a pair of spring conducting members interposed between said sheath lengthwise thereof and the opposite sides of said v resistance coil, said spring conducting members having fiat-sided portions conforming respectively to the opposite flat sides of said resistance coil and fin portions projecting from the flatsided portions thereof and conforming to the interior surface of said sheath.

5. In a resistor bulb adapted for response to changes in the temperature of a medium to which thebulb is exposed: the combination of a tubular protective sheath for immersionin said medium; a flat bar strip of core material within said sheath extending lengthwise of the latter; a resistance wire element wound on said core strip; and a pair of metallic spring conducting members secured to said core element and each comprising a thin flat strip having arcuate fins at the sides thereof, said conducting members being interposed between said resistance element and said sheath with the flat portions thereof conforming respectively to the opposite flat sides of said resistance element and with the fin portions conforming to the interior surface of said sheath, said fin portions being biased to exert pressure against said sheath and maintain the conducting members in close thermal association with said sheath and resistance element.

6. In a resistor bulb adapted for response to changes in the temperature of a medium to which the bulb is exposed: the combination of a tubular sheath for immersion in said medium, said sheath said core; spring conducting members secured to said core at the inner end thereof and interposed yieldably between said resistance element and said sheath, said spring members being yieldable in their thickness dimensions; an insulating member mounted removably in said mounting base; and means anchoring said core to said insulating member, said insulating member, core and resistance and conducting elements constituting a permanent assembly mountable into and removable from said sheath as a unit.

7 A resistor bulb comprising a metallic sheath of material having a thermal conductivity at most of the order of .07 calorie per degree C. per square cm. per cm. per second; a resistance element within said sheath, said element being spaced from said sheath and extending lengthwise thereof; and metallic conducting members interposed between said resistance element and said sheath, said conducting members being made of a material having a thermal conductivity at least of the order of .5 calorie per degree C. per square cm. per cm. per second, and the heat capacity of said conducting members being a minor fraction of that of said metallic sheath.

8. A resistor bulb comprising a metallic sheath of material having a thermal conductivity at most of the order of .07 calorie per degree C. per square cm. per cm. per second; a resistance element within said sheath, said element being spaced from said sheath and extending lengthwise thereof and metallic conducting members interposed between said resistance element and said sheath, said conducting members being made of a material having a thermal conductivity at least of the order of .9 calorie per degree C. per square cm. per cm. per second, and the heat capacity of said conducting members being a minor fraction of that of said metallic sheath.

9. A resistor bulb comprising a tubular metallic sheath; a resistance element in said sheath spaced from the wall thereof and extending lengthwise thereof; and metallic conducting means interposed yieldably between said resistance element and said sheath, said conducting means having a thermal capacity which is a minor fraction of the thermal capacity of said sheath.

10. In a resistor bulb adapted for response to changes in temperature of a medium to which the bulb is thermally exposed, and including an enclosing casing: the combination of a resistance coil in said casing, said coil having a substantial portion of the surface thereof spaced from the wall of said casing; a frame structure for said coil; and a resilient heat-conducting member interposed between said coil and said casing, said member being secured to said frame structure at one point only.

11. In a resistor bulb adapted for response to changes in temperature of a medium to which the bulb is thermally exposed, and including a tubular enclosing casing: the combination of a flat resistance coil in said casing; a frame structure for said coil; and a pair of resilient heat-conducting members interposed between the opposite flat sides of said coil and said casing, said members having flat portions conforming to the opposite flat sides of said coil and curved side fin portions conforming to the interior surface of said casing, said members further having strips extending from the flat portions thereof beyond said side fin portions; and means connecting said strips to said frame structure.

12. A resistor bulb adapted for response to changes in temperature of a medium to which the bulb is thermally exposed, comprising a casing, a resistance element inside said casing and spaced from the walls thereof; and a resilient heatconducting means thermally associated with said resistance element and in direct contact with a wall of said casing, said heat-conducting means exerting pressure against both said resistance element and said casing.

13. In a resistor device adapted for response to changes in temperature of a medium to which the device is thermally exposed: the combination of a casing; a temperature-responsive resistance element within said casing and spaced from the walls thereof; and compressibly yieldable heatconducting spring means interposed under pressure between said resistance element and the walls of said casing.

14. In a resistor device adapted for response to changes in temperature of a medium to which the device is thermally exposed: the combination of a casing; a temperature-responsive resistance element within said casing and spaced from the walls thereof; and heat-conducting means between said resistance element and casing and directly contacting the latter, said heat-conducting means having a mechanical connection to said resistance element at one point only.

FREDERICK G. KELLY. 

